In order to efficiently access necessary parts among various contents such as lengthy video or voice, there is a technology of attaching hierarchical tags on the contents to display a hierarchical structure of the tags. According to this technology, by tracing a hierarchical tag, a user can acknowledge the outline of the contents and can quickly find necessary parts.
In a case where a large amount of time-series texts such as meeting archives or records of call-takings at a call center are analyzed, in order to facilitate acknowledging of the topic of necessary parts and searching of parts corresponding to a specific topic, it is effective to display tags indicating the topics of time-series texts. However, in conventional technologies, because hierarchization of tags is fixed, it is not possible to display tags indicating the topics of time-series texts with an arbitrary scale specified by a user, and this problem requires improvements.